GB2153999A

GB2153999A - Remote temperature measurement

Info

Publication number: GB2153999A
Application number: GB08501513A
Authority: GB
Inventors: James Alan Mcknight; Iain Donald Macleod; Eric John Burton
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1984-02-03
Filing date: 1985-01-22
Publication date: 1985-08-29
Also published as: GB8402920D0; GB2153999B; US4655992A; DE3502879A1; JPS60183532A; GB8501513D0; FR2559260B1; FR2559260A1

Description

1 GB 2 153 999A 1

SPECIFICATION

Remote temperature measurement This invention relates to ultrasonic tempera- 70 ture measurement.

The invention has arisen in consideration of the severe problems that arise in measuring temperature of coolant flowing in a fast-fission nuclear reactor cooled by liquid sodium. Mon itoring of coolant temperature is not only vital for normal control purposes but it is also vital for safety purposes as temperature trends and transients can foreshadow the onset of inci dents like blockage of coolant flow which 80 might cause solid nuclear fuel to melt if corrective or preventative action is not taken.

Various solutions to these problems have been considered such as reliance on flowmeter or thermocouple readings or by the acoustic de tection of coolant boiling. However, with these known solutions uncertainties may arise especially where the normal flow is low, or there is cross-flow in which a normal flow could mask an abnormal flow. These uncer tainties are increased when, as is often the case, the flow or temperature measuring de vice cannot be located precisely at the most sensitive localities (which are usually the dis charge points of flow from defined channels into bulk zones) because of access or obstruc tion problems.

Whilst, current practice does not itself in volve any hazards, as the acceptable margin of safety can be suitably achieved, improved standard is continuously being sought. The present invention provides such an improved standard by the use of ultrasonics which may either replace or work in harness with known systems.

The use of ultrasonic techniques to measure temperature is well known-see, for example, British Patent Specifications Nos. 2114299,

2002118,1300159,1202182,1178529, 1178385 and 1035763. Patent No 1300159, for instance, is specifically concerned with a device for ultrasonic measurement of the temperature of liquid metal coolant within a nuclear reactor. Such a device suffers from the drawback that it is invasive in the sense that the hardware is physically lo cated at the position at which the temperature measurement is to be made and therefore interferes with the flow conditions prevailing at that position.

According to the present invention there is provided a method of measuring temperature within a body of fluid in which ultrasound is transmitted through the fluid and the time taken for the ultrasound to traverse a known distance is translated into a corresponding temperature value, said method being characterised in that, to measure temperature at a selected zone or zones within said body of elements located at a known separation distance or distances within a containment structure for said body of fluid:

a) ultrasound is launched into the fluid medium at a location which is physically discontiguous with said zone(s) whereby the ultrasound propogates towards said zone(s) and undergoes reflection by said elements; and b) the resulting ultrasound echoes are iden- tified as being derived from a particular zone or zone(s) and the elapsed time therebetween is translated into a temperature value.

The invention takes as its starting point the known fact that the sonic velocity in sodium (or other liquid for that matter) is a function of its temperature. The invention uses ultrasound beams from an interrogating ultrasonic transducer or transducers which can be sighted on said elements (for example the opposite sides of a channel containing nuclear fuel swept by sodium coolant or reflectors specifically in the channel). By measurement of the time difference between echoes received back from the elements demarcating each zone, together with a knowledge of the distance apart of the elements, sonic velocity can be calculated and hence the mean temperature between those points determined. It is also possible, because of the short time required to make a measure- ment, to monitor temporal fluctuations ("temperature noise" as it is sometimes called) which is a sensitive method of detecting local overheating. The beams from the interrogating transducers may be sighted to be pene- trating or to be at a glancing incidence, the latter being very advantageous for measuring temperatures at an outlet from a channel.

Where a number of zones lie on a common line which can be sighted along by a single interrogating transducer beam, it is possible for a number of temperature measurements to be taken and presented or recorded simultaneously.

Interrogating transducers may be individual to each zone, or they may be arranged, eg. on a sweep arm, so as to scan a multiplicity of zones.

The invention will now be described further with reference to the accompanying drawing in which:

Figures 1 and 2 are diagrams in plan and elevation respectively showing operation of the invention by glancing incidence on sur faces naturally present; Figure 3 is a plan view of a fast reactor fuel assembly in which temperature measurement of the breeder sub-assemblies at the periphery of the core are monitored; Figure 4 is a diagrammatic plan view illus trating scanning of the top portion of a single sub-assembly; Figure 5 is a graph showing variation of echo intensity with the incident angle 0 of the scanning beam; fluid, which zone or zones are demarcated by 130 Figure 6 is a block diagram of electronic 2 GB 2 153 999A 2 circuitry for use in the method of the inven tion; Figure 7 is a diagram showing operation of the invention using specifically provided reflectors.

Figure 8 is an isometric view of a sub assembly top portion; and Figure 9 illustrates diagrammatically an al ternative embodiment similar to Figure 7 but employing structural parts of the sub-assem- 75 bly as reflectors.

In Figures 1 and 2 of the drawings, the upper portions of a number of fuel or breeder sub-assembly wrappers or channels 10 are shown which each discharge liquid sodium coolant into a bulk volume 11. An interrogat ing ultrasonic transducer 12 immersed in liquid sodium in the bulk volume 11 emits a beam 13 of ultrasonic pulses which is narrow as viewed in Figure 1 but wider as viewed in Figure 2. This beam glances over the outlet ends of the channels 10 and returns echoes from diametrically-opposed edges 1 OA and 1 OB on each channel. The edges can be considered as locality point pairs. By measur ing the time intervals tl, t2 and t3 and with knowledge of the diameter of the channels, it is possible to resolve the mean temperature of sodium issuing from the outlets of the chan nels 10 non-invasively and before any signifi cant cross-flow can take place.

Figure 3 shows a plan of a fast reactor core comprising a hexagonal array of fuel and breeder material sub-assemblies. The upper parts of the fuel or breeder sub-assemblies are 100 of cylindrical shape, their lower ends termi nate in spikes for engagement in a diagrid structure of the reactor and they are of hexa gonal section over the remaining length. The inner sub-assemblies are assigned to reactor fuel and control devices, the outer three 1 rings' of sub-assemblies, ie. those outside the phantom line 50, are assigned to breeder fuel. The construction of the reactor in this embodiment may be such that the tempera tures of the inner sub-assemblies are mea sured by thermocouples, whereas the breeder sub-assembly temperatures are to be mea sured by ultrasonics.

As shown, a device S is provided for emitt- ing two ultrasonic beams, B1 and B2. It may comprise wavEiguides or immersed trans ducers suitable for sodium and operating in transmit-receive mode. The beams are made to sweep over the outer breeder sub-assem blies by oscillating the device S clockwise and anticlockwise alternately. A device similar to S may be placed at every vertex (or every alter nate vertex) of the hexagonal array, so that the devices S may collectively scan all of the breeder sub-assemblies by means of beams B1 and B2.

In order to understand the function of the electronics used to realise the measurement, the problem of examining the echoes from 130 one sub-assembly will be described with reference to Fig. 4. The ultrasonic beam from the scanning source S gives rise to echoes as a result of reflection from the 'high spots' on the sub-assembly top at D1 and D2. The echo times T1 and T2 are to be measured so that their difference can be computed for the temperature determination. By knowing the angle of direction 0 of the beam from some known reference direction, and from the pulse-echo times, it is possible to calculate the location of the high spots D 'I and D2 (ie. points at which the reflecting surfaces are normal to the beam), and plot them as an ultrasonic image of the area. In practice, because of the divergence of the beam, the image obtained of the high spots would be two 'streaks', 11 and 12. It should be noted that whilst the image is streaked, the echoes always arise from the high spots, but these may reflect from edge rays of the actual sonic beam.

The exact orientation of the high spots may be determined by examining the intensity 1 of the reflected signal. Fig. 5 shows how this would vary with the direction of the beam for one high spot, D1. The maximum signal is obtained when the central ray of the beam is pointing directly at the high spot, and so the orientation of the point D1 can be determined in terms of the angle 0. The time difference T1-T2 between the signals from both D1 and D2 provides an indication of the sonic velocity, and hence fluid temperature, whether the echoes arise from the central ray of the beam or not. In most cases this would be true, but when the beam is not pointing directly at the high spots, it may also be reflecting from an adjacent sub-assembly, and confusion between signals may occur. Consequently the need to identify when the echoes are coming from a correctly pointed beam.

The electronic system to identify the echoes and report deduced temperatures is shown diagrammatically in Figure 5. The scanner S is driven in its oscillatory motion by a motor 52 which may be a stepping motor. For this example, however, the motor is considered free-running. A position encoder 54 on the mechanical drive enables the direction (8) of the scanning transducer S to be determined at anytime. The controlling processor 56 (Intel 8086) loads a waveform generator 58 (Namlak type VHR 2195) with data for driving a selected one of the transducers with the opti- mum pulse shape for accurate timing of echoes. The waveform is then passed to the selected transducer through a multiplexer to a transducer driver 62. The returned echo signals received by the transducer are passed through a pre-amplifier 64 via a multiplexer 66 to a logarithmic response amplifier 68. This has a dynamic range of typically 60-70 db, allowing the entire range of reflected echoes to be accommodated. The individual echoes from targets in the path of the ultra- 3 sonic beam are detected by the peak detector 70, which then interrogates a timing clock 72 to obtain a timing for each echo. The ampli tude of the echo is digitised by an analogue to digital convertor 74. The entire data for each 70 echo, viz its digitised amplitude, its time since pulsing of the respective transducer, and the position of the scanner S at the time of echo reception are all stored temporarily as a single data 'word' in a First-In-First-Out store (FIFO) 75 76. Each succeeding echo has its data placed sequentially into the store.

After about 2 milliseconds all echoes of interest from a particular transducer transmit pulse will have been received, but a further 5 milliseconds (say) will elapse before all spuri ous echoes will have died away, and the same, or an adjacent transducer may then be pulsed. During this period, the data in the FIFO 76 is extracted and interpreted. The approximate location of the wanted echoes will, of course, already be known. A data processor (Intel 8086) 78 recognises the wanted echoes, and stores the precise ampli tude and timing data for each in an appropri ate table in a random access memory 80. This memory, in effect, stores all the data for all the 'streak' images described earlier in tabu lated form. As the scanning device S moves, and the transducers are pulsed, these tables are updated with the latest information. When the FIFO 76 is empty, the controlling proces sor 56 prepares and fires the next transducer pulse.

The random access memory 80 that stores the echo tables is of two-port form. An analys ing processor 82 (Intel 8086) examines these tables, deduces the maximum signal for a particular echo (ie. the peak of a 'streak', cf.

Fig. 5), calculates time differences between appropriate echoes, and temperatures for spe cific fuel assemblies. The processor 82 may operate independently of the remainder of the system so that it can apportion its time to suit various purposes. For example, it can devote more time to examining the temperature varia tions (temperature noise) of a particular sub assembly, or more time to the more critical breeder sub-assemblies. It may, of course, apply different significance to the tempera tures deduced for different assemblies, eg.

apply a different threshold for instituting dif ferent types of output signal (eg. alarm sig nals) for alerting operators and/or automatic control of the reactor.

An output processor 84 (Intel 8087) via output lines 86 may drive alarm and possibly reactor shut-down facilities. In addition, vari ous displays and hard-copy output for infor mation and experimentation may be provided 125 via the output lines 86.

In Figure 7 a fuel channel 30 is fitted internally with two reflectors 30A, 3013. These are interrogated by an ultrasonic beam 33 from a transducer 32 enabling temperature or 130 GB 2 153 999A 3 temperature noise in the region of the channel between the reflectors to be measured. Reflector 30A has a horizontal face (so that some of the beam 33 is reflected back along its path of incidence) and an inclined face (so that some of the beam 33 is reflected to reflector 30B). Reflector 30B simply has an inclined face.

Figure 8 shows a general view of the top portion of a fast reactor subassembly 90, and identifies the top edge 9 1 (Vvhich forms the outlet of the sub-assembly and may be castellated), an orientation bar 92, a burst pin detection pipe 94, and a plate 96 which retains the breeder fuel. As shown in Figure 9, a transmit-receive transducer 98 can be located (as indicated by arrows 100) from two or more of these features. Thus it is possible to obtain the time difference, and hence tem- perature information required since the separ- ation distances between the targets 91, 92, 94 and 96 will be accurately known. Thus, a transducer can be placed to obtain echoes from all four targets simultaneously.

In each of the embodiments described, it will be noted that the ultrasound source is physically discontiguous with the zone or zones at which temperature measurements are to be made, ie. in the sense that the ultrasound is coupled from a remote location to the zone or zones through the fluid itself without relying on any intermediary structure which would otherwise interfere with fluid flow through such zones.

Claims

1. A method of measuring temperature within a body of fluid in which ultrasound is transitted through the fluid and the time taken for the ultrasound to traverse a known distance is translated into a corresponding temperature value, said method being characterised in that, to measure temperature at a selected zone or zones within said body fluid, which zone or zones are demarcated by elements located at a known separation distance or distances within a containment structure for said body of fluid:

a) ultrasound is launched into the fluid medium at a location which is physically discontiguous with said zone(s) whereby the uitrasound propogates towards said zone(s) and undergoes reflection by said elements; and b) the resulting ultrasound echoes are iden- tified as being derived from a particular zone or zones and the elapsed time therebetween is translated into a temperature value.

2. A method as claimed in Claim 1 in which said elements are constituted by structural parts of said containment structure.

3. A method as claimed in Claim 1 in which said elements are constituted by reflectors attached to structural parts of said containment structure.

4. A method as claimed in Claim 1 in which 4 GB 2 153 999A 4 said containment structure includes an array of generally parallel fluidconducting channels having generally coplanar outlets and in which the ultrasound is propagated generally traversely of the fluid flow from said outlets at glancing incidence to said outlets whereby reflections occur at diametrically-opposed edge portions of the outlets, which edge portions constitute said elements.

5. A method as claimed in Claim 1 in which said containment structure includes an array of generally parallel fluid-conducting channels having generally coplanar outlets and in which the ultrasound is propogated generally length- wise of said channels whereby reflections occur at stuctural parts, or reflector-carrying structural parts, within the channels.

6. A method as claimed in any one of Claims 1 to 5 including scanning the ultra- sound across the containment structure to derive echo signals from a multiplicity of zones within the structure and analysing the received echo signals to associate them with respective zones. 25

7. A method as claimed in any one of Claims 1-6 in which said containment structure comprises a nuclear reactor utilising a liquid metal coolant which constitutes said fluid.

8. A method of measuring temperature substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935- 1985. 4235 Published at The Patent Office, 25 Southampton Buildings. London, WC2A 1 AY, from which copies may be obtained -